1. Field of the Invention
Aspects of the present invention relate to an organic light emitting diode (OLED) display device, and more particularly, to a double-emission OLED display device which has two bonded substrates including independently-drivable OLEDs, respectively, and displays images at double sides, in such a way that breakage by external impact and power consumption can be reduced.
2. Description of the Related Art
Cathode-ray tube display devices are being replaced by flat panel display devices that are light and compact. The flat panel display devices include liquid crystal display (LCD) devices and organic light emitting diode (OLED) display devices. Among them, the OLED display devices have excellent brightness and a wide viewing angle. Further, the OLED display devices do not need a backlight unit and can be manufactured in a very compact size.
The OLED display device is a display device which emits light of a specific wavelength when electrons and holes combine with each other in an organic thin layer from a cathode and an anode to create excitons, and the excitons transition from an excited state to a ground state.
The OLED display device may be classified into a passive matrix OLED display device and an active matrix OLED display device depending on the driving method. The active matrix OLED display device has a circuit using a thin film transistor (TFT). The passive matrix OLED display device may be fabricated using a simple process since anodes and cathodes are arranged in a matrix on a display region. However, the passive matrix OLED display device is generally applied only to low-resolution, small-sized display devices due to the resolution limit, a high driving voltage, and short lifetimes of materials. In the active matrix OLED display device, a display region includes a thin film transistor for each pixel, and an equal amount of current is applied to the pixels, so that uniform brightness can be obtained. Moreover, the active matrix OLED display device may be used as a high-resolution large-sized display due to low power consumption.
Further, the OLED display device may include independently-drivable OLEDs formed on respective substrates to display different images in opposite directions. However, such a double-emission organic light emitting diode (OLED) display device includes two substrates having independently-drivable OLEDs, respectively. Here, the substrates are bonded to allow OLEDs to be spaced apart from each other. Because of such a structure, the OLEDs can be easily broken by pressure externally applied to the substrate in a vertical direction. Moreover, for independent drive, each OLED has a power voltage line, and thus the OLED display device has a complicated arrangement of interconnections and increased power consumption.